1. Field of the Invention
The present invention relates to a scheme for intermittent reception of paging signals in a mobile communication system in which a receiver circuit of a mobile station is operated intermittently in order to reduce the battery power consumption at the mobile station in a state of waiting for paging signals from a base station, so that the mobile station receives the paging signals from a base station intermittently. The present invention also relates to a base station apparatus and a mobile station apparatus which are suitable for realizing this scheme for intermittent reception of paging signals in a mobile communication system.
2. Description of the Background Art
In a mobile communication system, in order to carry out the intermittent reception of paging signals at the mobile station, the mobile stations are divided into groups and each mobile station identifies a control channel determined according to the group assigned to this mobile station and a paging channel (PCH) in that control channel, so as to realize the intermittent reception by receiving only the paging channel (PCH) of the own group.
According to the grouping of the mobile stations in the digital mobile communication system called PDC (Personal Digital Cellular) which is currently used in Japan, a frequency number (a radio channel position number) IF and a PCH group number IP for specifying a control channel and a paging channel to be identified by the mobile station are defined as follows: EQU n'=(n-1)mod(NC.times.NP)+1 EQU IF=(n'-1)mod NC+1 EQU IP=[(n-1)/NC]+1
where n is an ID information of the mobile station, NC is a number of control channels within a zone (cell), NP is a number of PCH groups within a control channel (superframe), and [X] denotes the maximum integer not exceeding X.
As a concrete example, the grouping in a case of using three control channels as shown in FIG. 1 will be described. In FIG. 1, there are three control channels identified by their frequency numbers (slots) F1 (S), F2 (S) and F3 (S), so that NC=3. The paging channels (PCH) are divided into nine groups P1 to P9, and a number of PCH groups within each control channel is NP=3. In this case, for the mobile station ID information n=9, the frequency number IF and the PCH group number IP can be calculated as follows. EQU n'=(9-1)mod(3.times.3)+1=9 EQU IF=(9-1)mod(3+1)=3 EQU IP=[(9-1)/3]+1=3
Consequently, the control channel to be used by this mobile station is the third one F3 (S), and the PCH group of this mobile station in this control channel is the third one P9. Therefore, it suffices for this mobile station to intermittently receive the paging channel P9 of the ninth group alone.
In other words, the mobile station which is classified into the first group according to its mobile station ID information is required to intermittently receive the paging channel P1 of the first group alone and identify paging signals contained within that paging channel P1, the mobile station which is classified into the second group according to its mobile station ID information is required to intermittently receive the paging channel P2 of the second group and identify the paging signals contained within that paging channel P2, and so on. Note that, in FIG. 1, B represents the broadcast channel (BCCH), and SC represents the signalling control channel (SCCH) for the cell specific information.
As described above, the ON/OFF timing of a receiver circuit of the mobile station in a case of the intermittent reception is specified within a 720 ms superframe formed by 36 frames as shown in a part (a) of FIG. 2. In the PDC, the reception time of the paging signals is partitioned by time-slots and the 3-channel TDMA is used so that, in FIG. 2, the broadcast channel (BCCH) (represented by B in FIG. 2) occupies two time-slots and the paging channel (PCH) (represented by P in FIG. 2) of the mobile station which is classified into a specific group is provided at one timeslot following these broadcast channels.
By means of the grouping within such a superframe, the mobile station turns the power of the receiver circuit ON only during a period corresponding to the broadcast channel B and a period corresponding to the paging channel P of the own group as indicated in a part (b) of FIG. 2, so as to intermittently receive only the paging signals within that paging channel P.
In this case, a time rate for turning the power of the receiver circuit of the mobile station ON, i.e., the intermittent rate, is given in terms of a number of BCCH time-slots Ab and a number of PCH time-slots Ap, as follows: ##EQU1##
A smaller value of this intermittent rate, i.e., the power ON time rate, implies a smaller rate for the consumption of the battery power of the mobile station.
As described above, the mobile station reduces the battery power consumption by carrying out the intermittent reception of the paging signals, but in order to reduce the battery power consumption further, it is necessary to make the above described intermittent rate as small as possible, and there is still a demand from the mobile station user's viewpoint for a further reduction of the battery power consumption.